Block air and moisture to make stucco last

A member of the Holmes team applies stucco to a house's exterior.

Photograph by: Alex Schuldt/Handout
, The Holmes Group

Traditionally stucco has been a popular exterior wall system. It adds character and can give a house a sophisticated finish - especially when it's combined with other masonry wall systems like brick. And, if it's done right, stucco can also be a great barrier against rain and snow and provide extra insulation.

The big problem with stucco is that it doesn't work great in all environments. It works best in dry climates, because if it's exposed to moisture it can start to crumble. Have you ever seen an old building with crumbling stucco walls? Not pretty. It's also a pain to fix because you're not dealing with just one layer.

Because stucco has many layers, fixing it usually requires tackling all those other layers. It take time, and it's expensive. A stucco exterior on a home can cost $30,000 to $40,000, sometimes more. That's why you mainly see stucco on homes in hot, dry climates, like in the southern US where it generally lasts longer. But there are a couple of strategies that help preserve stucco in climates such as those across Canada.

First, you don't want a stucco wall to have snow resting against it. If you've seen a house or building that has a stucco exterior from top to bottom, you might see it crumbling or flaking wherever it's been most exposed to moisture. In most cases, that's along the bottom of a house where moisture from the ground, precipitation and snow will sit.

That's why if we're doing stucco I like to have a masonry bottom and a stucco finish at the top of the house - usually on the second floor. Keeping stucco away from the ground helps prolong its life.

The second strategy is controlling the air and moisture behind the stucco finish.

As I've said before, stucco has many layers. The first layer is the substrate - the material the stucco is applied to. This material must be tough and durable. A product such as oriented strand board (OSB) works best, but plywood sheathing is also effective.

On top of the substrate is the air and moisture barrier, probably the most important layer. Some people call it water/moisture/weather material. The purpose of this layer is to prevent moisture from penetrating through to the substrate material that's vulnerable to moisture, like wood sheathing or gypsum. If moisture gets trapped there it can start to rot the material and damage the stucco finish on the surface.

Depending on local code or manufacturer's instructions, or both, there might be specific moisture barrier and assembly requirements. Always check what they are and verify it with your contractor. In my line of work asking questions rarely leads to problems. It's when homeowners don't ask enough questions that things get messy.

Some contractors will use waterproof building paper as the air and moisture barrier. If that's the case vertical seams should be overlapped by 6 inches (15 cm) or more; horizontal seams by 4 inches (10.2 cm) or more. But my guys apply an air and moisture barrier that looks a lot like icing on a cake. There are no seams so it provides one solid layer of protection.

The traditional way of doing stucco requires a steel mesh that's properly installed on top of the moisture barrier. Then the stucco is applied-two layers if you're working over masonry or concrete (one base coat, one finish coat). Three layers if it's going over wood framing (scratch coat, base coat and finish coat). But there are a couple of new systems out there that have changed the process.

We now have exterior insulation finish systems (EIFS) that are basically rigid foam panels that go over the moisture barrier. I like them for two reasons: It gives us extra insulation and increases the R-value (resistance to heat loss) of your exterior walls. Two, these systems can help drain any moisture caught behind the stucco layers.

On a recent job we used a type of EIFS called PUCCS (pressure-utilized compartmented cavity system). PUCCS insulation is flat on one side with puck-looking shapes on the other Ð go figure. The side with the puck shapes goes against the air and moisture barrier. So in case moisture gets in it flows through the cavities in between all the pucks and finds its way to the bottom of the wall where the drainage track is.

There's so much to consider when it comes to stucco. Every tradesperson will have a different way of doing it. But the most important thing to keep in mind is to follow the manufacturer's instructions on all the materials. If they aren't followed the manufacturer's warranty can be compromised, so if there was a problem you'd be out of luck and stuck with the repair bill. Be smart. Be involved. And ask questions to make sure your home's stucco stands the test of time.

Catch Mike Holmes in his new series Holmes Makes It Right Tuesdays at 9 p.m. on HGTV. For more information, visit hgtv.ca. For more information on home renovations, visit makeitright.ca.

We encourage all readers to share their views on our articles and blog posts. We are committed to maintaining a lively but civil forum for discussion, so we ask you to avoid personal attacks, and please keep your comments relevant and respectful. If you encounter a comment that is abusive, click the "X" in the upper right corner of the comment box to report spam or abuse. We are using Facebook commenting. Visit our FAQ page for more information.

Latest updates

Cariwest Think of Cariwest as a very concentrated Heritage Days, one that focuses exclusively on Caribbean culture. Churchill Square will turn into a Caribbean Village for the run of the festival, which promises music, art, dance and food. The Cariwest parade starts at noon on Saturday, beginning at the Legislature building, then heading down 109th Street to Churchill Square. A smaller children’s parade happens at the square on Sunday at 1 p.m.